Self-venting cap for a neck of a dewar vessel

ABSTRACT

A self-venting cap for a neck of a dewar vessel with a lower component having a first plurality of apertures, an upper component with a second plurality of apertures, a seal held between the lower and upper components, and a third component releasably secured to the upper component. The cap forms a compression seal about an inner circumference of the neck of a dewar vessel when the lower and upper components are matingly engaged in a sealing position, creating a plurality of tortuous vapor paths through the cap. When the cap is in the sealing position, a first chamber is formed between the lower and upper components and a second chamber and a vent opening are formed between the upper and third components. In this position, vapor inside the dewar vessel can travel in a plurality of tortuous paths beginning within the neck and then sequentially travelling up through the first plurality of apertures, the first chamber, the second plurality of apertures, the second chamber and then out the vent opening. There can also be a plurality of shorter tortuous paths beginning within the first plurality of apertures, travelling through the first chamber, and then up through at least two of the second plurality of apertures. A semi-permeable membrane, which can be incorporated in the cap, prevents moisture from entering into the dewar vessel while still allowing vaporous cryogen to exit from the dewar vessel.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation of U.S. patentapplication Ser. No. 09/753,194, filed Dec. 29, 2000, the disclosure ofwhich is specifically incorporated herein by reference, and is otherwiseidentical to the disclosure of U.S. patent application Ser. No.09/753,195, now abandoned. The present application is related to U.S.patent application Ser. Nos. 09/753,208 and 09/753,207, both of whichwere filed on Dec. 29, 2000, the disclosures of which are specificallyincorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention is in the field of cryogenic shippingcontainers.

BACKGROUND OF THE INVENTION

[0003] To ensure reproducible results in research and biotechnicalprocesses, today's scientists and clinical practitioners have found itnecessary to genetically stabilize living cells and preserve theintegrity of complex molecules for storage and transport. This isaccomplished by containing these materials in enclosures where cryogenictemperatures are continuously maintained at or near liquid nitrogen orvapor phase liquid nitrogen temperatures (77K and 100K, respectively).

[0004] Advances in cryopreservation technology have led to methods thatallow low-temperature maintenance of a variety of cell types andmolecules. Techniques are available for the cryopreservation of culturesof viruses and bacteria, isolated tissue cells in tissue culture, smallmulti-cellular organisms, enzymes, human and animal DNA, pharmaceuticalsincluding vaccines, diagnostic chemical substrates, and more complexorganisms such as embryos, unfertilized oocytes, and spermatozoa. Thesebiological products must be transported or shipped in a frozen state atcryogenic temperatures to maintain viability. This requires a shippingenclosure that can maintain a cryogenic environment for up to 10 daysand meet other shipping requirements such as being relatively imperviousto mechanical shock and effects of directional orientation.

[0005] In addition to the already existing difficulties posed inshipping heat-sensitive biologicals, the International Air TransportAssociation (IATA) imposed new regulations which became effective inJanuary 1995 pertaining to all shipments that include specimenscontaining infectious agents or potentially infectious agents. Theseregulations, endorsed by the U.S. Department of Transportation (DOT) andapplicable to all public and private air, sea, and ground carriers,imposed greatly increased requirements upon shipping units to surviveextensive physical damage (drop-testing, impalement tests, pressurecontainment tests, vibration tests, thermal shock, and water damage)without leakage and without fracture of the internal, primaryreceptacles (vials). Implementation of this regulation furthercomplicated the shipping of frozen biologicals.

[0006] Even though bioshippers are currently available using liquidnitrogen as a refrigerant, little innovation has taken place in thedesign of packaging for low-temperature transport. Current shippers aregenerally vulnerable to the physical damage and changes in orientationencountered during routine shipping procedures. Additionally, theseshippers rarely comply with the IATA Dangerous Goods Regulation(effective January 1995 or as later amended). Commercial vendors havenot developed or certified a cost-effective, standardized shipping unitwith the necessary specimen capacity and hold time to meet user demands.

[0007] One of the main criticisms of current shippers is price, whichvaries from $500.00 to $1,000.00 or more per unit. This substantiallylimits their use for the transport of many biologicals. Because of theinitial cost and limited production of these containers, they aredesigned to be reusable. However, the cost of return shipping of theseheavy containers is significant, particularly in international markets.

[0008] Users also complain about the absorbent filler used in thecurrent dry shippers, which breaks down with continuous use,contaminating the interior of the container. In fact, one large user ofthese containers has essentially centered their entire shippingoperation around cleaning the broken down absorbent material from theinside of these containers after each use.

[0009] Another problem cited by users of currently available dryshippers relates to the functional hold time versus static hold time.Static hold time pertains to a fully charged shipper with no heat load,sitting upright, e.g., essentially not in use. Functional hold timerefers to the fully charged shipper in use and containing samples, e.g.,in the process of being handled and transported. Even though the statichold time is promoted as being 20 days, if the container is tilted orpositioned on its side, the hold time diminishes to hours as opposed todays. This occurs because the liquid nitrogen transitions to the gaseous(vapor) phase more rapidly resulting in outgassing. The liquid nitrogencan also simply leak out of the container when it is positioned on itsside.

[0010] The current cryogenic containers are promoted as being durablebecause they are of metal construction. However, rugged handlingfrequently results in the puncturing of the outer shell or cracking atthe neck, resulting in loss of the high vacuum insulation. This rendersthem useless. The metal construction also adds to the weight of thecontainer, thereby adding substantially to shipping costs.

[0011] Thus, there is a need for an improved cryogenic container thatcan be used to ship biologicals safely, reliably, and economically.

[0012] U.S. Pat. No. 6,119,465 seeks to meet this need by using unique,lightweight, low-cost, durable composites and polymers in asemi-disposable vapor phase liquid nitrogen bioshipper. This isaccomplished in an inherently simple, reliable, and inexpensive devicethat will result in reduced shipping costs, enhanced reliability andsafety, and fewer service requirements.

[0013] The present invention builds upon the framework laid by U.S. Pat.No. 6,119,465, the disclosure of which is specifically incorporatedherein by reference. Creating a self-venting cap that leads to a morereliable, while still economical, cryogenic shipping container doesthis.

SUMMARY OF THE INVENTION

[0014] The present invention is generally directed to a self-venting capfor a neck of a dewar vessel. The cap has a lower component with a firstplurality of apertures, an upper component with a second plurality ofapertures and a seal held between the lower and upper components. Thecap is capable of forming a compression seal about an innercircumference of the neck of a dewar vessel when the lower and uppercomponents are matingly engaged in a sealing position. When acompression seal is created, there is at least one, and preferably morethan one, tortuous vapor path through the cap to allow venting ofvaporous cryogen from within the dewar vessel.

[0015] In a first, separate aspect of the present invention, the cap hasa third component releasably secured to the upper component. When thecap is in the sealing position, a first chamber is formed between thelower and upper components and a second chamber and a vent opening areformed between the upper and third components. In this position, vaporinside the dewar vessel can travel in a plurality of tortuous pathsbeginning within the neck and then sequentially travelling up throughthe first plurality of apertures, the first chamber, the secondplurality of apertures, the second chamber and then out the ventopening. There can also be a plurality of shorter tortuous pathsbeginning within the first plurality of apertures, travelling throughthe first chamber, and then up through at least two of the secondplurality of apertures. The lower component has an outer circumferencethat is less than the inner circumference of the neck and its firstplurality of apertures is located inside of its outer circumference. Itis especially preferable that the vent opening and the outercircumference of the upper and third components are located outside ofthe inner circumference of the neck.

[0016] In still other, separate aspects of the present invention, thecap can be incorporated into a capped dewar vessel assembly, and thecompression seal can be strong enough to support the weight of the dewarvessel when it is not charged with a cryogen. A semi-permeable membranethat prevents moisture from entering into the dewar vessel while stillallowing vaporous cryogen to exit from the dewar vessel can beincorporated into the dewar vessel, and preferably within theself-venting cap.

[0017] In still further, other separate aspects of the presentinvention, a male and a female thread matingly engage the lower andupper components. The upper component can contain a positioning deviceon a lower surface capable of engaging with a second positioning devicelocated in a fixed position relative to the neck of a dewar vessel suchthat once the first and second positioning devices are engaged, rotationof the third component in a tightening direction will cause the seal tobe squeezed between the lower and upper components to form thecompression seal. It is especially preferred that the lower component,the upper component and the third component are made of cryogenicallycompatible material that is non-metallic and non-conductive. It is alsoespecially preferred that the seal is made of a cryogenically compatiblematerial, and more especially a silicone material. In addition, therecan be multiple vent openings in the cap.

[0018] Accordingly, it is a primary object of the present invention toprovide an improved, self-venting cap for use with a dewar vessel thatcan be charged with a liquid cryogen.

[0019] This and further objects and advantages will be apparent to thoseskilled in the art in connection with the drawings and the detaileddescription of the preferred embodiment set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is an exploded assembly drawing of a preferred embodimentof a portable, insulated shipping container according to the presentinvention with a containment system for dangerous materials.

[0021]FIG. 2 is a planar cross section with a partial cutaway view of apreferred embodiment of a portable, insulated shipping container.

[0022]FIG. 3 is an assembly drawing of a preferred embodiment of a dewarvessel assembly.

[0023]FIG. 4 is an exploded assembly drawing of a preferred embodimentof a self-venting cap taken from reverse directions.

[0024] FIGS. 5A-5C are a planar cross section of a preferred embodimentof a portable, insulated shipping container showing connection of apreferred self-venting cap.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The preferred embodiments of the present invention can be used aspart of an overall system that utilizes several inventions. Broadlyspeaking, there is an overall cryogenic shipping container system.Within the shipping container, there is a dewar vessel. Within the dewarvessel, there is a specimen chamber for holding specimens. Theself-venting cap of the present invention helps to securely holdspecimens within the cryogenic shipping container. Although FIGS. 1-5are described in greater detail below, the following is a glossary ofthe elements identified in the Figures:

[0026]1 portable, insulated shipping container

[0027]2 dewar vessel

[0028]3 outer casing of dewar vessel 2

[0029]3 a upper half of outer casing 3

[0030]3 b bottom half of outer casing 3

[0031]4 opening at top of outer casing 3

[0032]5 evacuable space between outer casing 3 and inner casing 13

[0033]6 getter pack

[0034]7 desiccant

[0035]8 nipple

[0036]10 layer of super insulation

[0037]11 dewar opening into inner vessel 13

[0038]13 inner vessel of dewar vessel 2

[0039]13 a upper half of inner vessel 13

[0040]13 b lower half of inner vessel 13

[0041]14 opening at top of inner vessel 13

[0042]15 inner wall of inner vessel 13

[0043]21 neck portion of dewar vessel 2

[0044]30 plastic foam

[0045]31 foam segment of plastic foam 30

[0046]32 capillarity separation layer of foam 30

[0047]40 outer shipping container shell

[0048]41 base of outer shipping container shell 40

[0049]42 side wall of outer shipping container shell 40

[0050]42 a top side wall of side wall 42

[0051]42 b top opening formed in top side wall 42 a

[0052]43 top wall of outer shipping container shell 40

[0053]44 handle molded in outer shipping container shell 40

[0054]45 pocket for paperwork formed in outer shipping container shell40

[0055]46 hinge mechanism

[0056]47 latch mechanism

[0057]48 certification plate assembly

[0058]48 a certification plate

[0059]48 b rivet for certification plate assembly 48

[0060]48 c indentation in outer shipping container shell 40 forcertification plate

[0061]50 support assembly for dewar vessel 2

[0062]51 bottom portion of support assembly 50

[0063]52 side rib portion of support assembly 50

[0064]53 top portion of support assembly 50

[0065]55 safety strap

[0066]56 adjustable buckle of safety strap 55

[0067]57 outer bottom of dewar vessel 2

[0068]60 funnel-shaped vessel plate

[0069]61 support for plate 60

[0070]62 spray foam

[0071]70 specimen chamber

[0072]71 side wall of specimen chamber 70

[0073]72 base of specimen chamber 70

[0074]73 top opening of specimen chamber 70

[0075]80 containment system

[0076]81 bag of containment system 80

[0077]83 porous structural cartridge of containment system 80

[0078]90 inner plug

[0079]91 handle of inner plug 90

[0080]100 self-venting cap

[0081]101 lower component of self-venting cap 100

[0082]102 upper component of self-venting cap 100

[0083]102 a lower surface of upper component 102

[0084]103 seal of self-venting cap 100

[0085]104 third component of self-venting cap 100

[0086]105 plate

[0087]106 screw (threads not shown)

[0088]107 cover plate

[0089]108 female thread in lower component 101

[0090]111 male thread

[0091]112 female thread

[0092]113 positioning device

[0093]114 second positioning device

[0094]115 rib

[0095]121 first plurality of apertures in lower component 101

[0096]122 second plurality of apertures in upper component 102

[0097]131 first chamber of self-venting cap 100

[0098]132 second chamber of self-venting cap 100

[0099]133 vent opening of self-venting cap 100

[0100]FIG. 1 provides an assembly drawing that illustrates all of thecomponents of the cryogenic shipping container, generally designated as1, in a disassembled state, and FIG. 2 illustrates how all of thesecomponents fit together in an assembled state. FIG. 3 is an assemblydrawing that illustrates how dewar vessel 2 is assembled. All of theseFigures, as well as the assembly of parts illustrated in these Figures,are described in detail in a patent application filed concurrentlyherewith, Attorney Docket No. JSF35.051, entitled “CRYOGENIC SHIPPINGCONTAINER, the disclosure of which is specifically incorporated hereinby reference. However, it is worth repeating, for the sake of clarityherein, that a dewar vessel has an outer casing and an inner vessel witheach having openings at their tops connected together by a neck portionforming an evacuable space between the outer casing and the inner vesseland a dewar opening into the inner vessel.

[0101]FIGS. 4A and 4B illustrate an especially preferred self-ventingcap 100 for use with a dewar vessel 2. The manner in which such a capfunctions in an especially preferred application of shipping container 1is illustrated in FIGS. 5A-5C. Self-venting cap 100 has four primarycomponents—a lower component 101 with a first plurality of apertures121, an upper component 102 with a second plurality of apertures 122, aseal 103, and a third component 104. It is especially preferred that allof these four primary components be constructed of a cryogenicallycompatible material that is non-metallic and non-conductive. The first,second and fourth components can be made of an injection moldablematerial such as Acetyl. The outer circumference of lower component 101is less than the inner circumference of neck 21 and the first pluralityof apertures 121 is located inside of the outer circumference of thelower component as shown in FIGS. 4A and 4B.

[0102] When self-venting cap 100 is assembled, seal 103, which ispreferably made of silicone rubber, is attached to lower component 101by a snap, friction fit. Lower component 101 is secured to uppercomponent 102 and third component 104 by two different means.

[0103] First, a screw 106 (threads not shown) is screwed into a femalethread 108 in lower compartment 101 and held in place by plate 105. Acover plate 107 (shown with a trademark of Cryoport, Inc.) covers andseals the chamber in third component 104 in which the top of plate 105and the head of screw 106 are held. Screw 106 holds all four primarycomponents together in a cap assembly in which the individual primaryparts can still move relative to each other. In this assembly, secondcomponent 102 is held between first component 101 and third component104, and seal 103 is held between first component 101 and secondcomponent 102.

[0104] Second, lower component 101 has a male thread 111 that screwsinto female thread 112 of third component 103. When male thread 111 isnot fully screwed into female thread 112, seal 103 is held in a tautposition (see FIG. 5B) relative to the position it is held when malethread 111 is fully screwed into female thread 112 in a compression sealposition (see FIG. 5C). Seal 103 changes position between FIGS. 5B and5C when third component 104, which functions as a crank top, is rotatedin a tightening direction that causes seal 103 to be squeezed betweenlower and upper components 101 and 102 so as to form a compression sealwith neck 21. (FIG. 5B shows cap 100 before it is in a compression sealposition while FIG. 5C shows cap 100 once it is in a compression sealposition.) Ribs 115 of third component 104 rest against upper component102, which serve as a stop, and thereby create a plurality of ventopenings, in the compression seal position. (The left half of FIG. 5Chas been slightly rotated to show a clear vapor path instead of such atop.) A positioning device 113 (shown as indentations in FIG. 4B) onlower surface 102 a of upper component 102 engages with a secondpositioning device 114 (shown as nubs in FIG. 1) to prevent cap 100 fromspinning during the tightening process.

[0105] When self-venting cap 100 forms a compression seal with neck 21of dewar vessel 2 (as shown in FIG. 5C), vapor flow between inner vessel13 and outside of dewar vessel 2 must flow through vent opening 133.FIG. 5C illustrates one such vapor path. The path includes flow througha first chamber 131 located between lower and upper components 101 and102, and a second chamber 132 located between second component 102 andthird component 104. Vent opening 133 can be a single opening or aplurality of openings. In FIG. 5C, vent opening 133 is located betweenthird component 104 and plate 60, but it could also be located betweenthird component 104 and neck 21 if plate 60 is not used. Vent opening133 is located outside of the inner circumference of neck 21 becauseupper component 102 has an upper outer circumference that is locatedoutside of the inner circumference of neck 21.

[0106] Self-venting cap 100 provides many advantages over traditionalcaps for dewar vessels.

[0107] One advantage of self-venting cap 100 is the strength of thecompression seal it forms with neck 21 of dewar vessel 2. The seal canbe strong enough to support the weight of dewar vessel 2 when it is notcharged with a cryogen, or even stronger. This degree of strength isimportant when container 1 is subjected to shock or impact because cap100 restricts access to, and effectively seals off access to, thecontents of specimen chamber 70 and specimen containment systems insideof dewar vessel 2.

[0108] Another advantage of self-venting cap 100 is that it creates aplurality of tortuous vapor paths for venting dewar vessel 2. A tortuousvapor path increases the thermal length that gas venting from the dewarvessel must travel. Increasing the thermal length increases the thermalefficiency of the dewar vessel, thereby increasing the hold time for theshipping container. Multiple venting paths increases safety because iteliminates the possibility that a single venting path might becomeclogged, leading to dangerous build-up of gas.

[0109] In the preferred embodiment of cap 100, each of the firstplurality of apertures 121 leads into first chamber 131, and each of thesecond plurality of apertures 122 leads out of first chamber 131 andinto second chamber 132. Thus, vapor inside of dewar vessel 2 can travelin a plurality of tortuous paths when cap 100 is in the compression sealposition. The plurality of tortuous paths begin within neck 21 and thensequentially travel up through first plurality of apertures 121, firstchamber 131, second plurality of apertures 132, second chamber 132 andthen out vent opening 133. In addition, because of the volume ofchambers 131 and 132, gas need not always leave the chamber at the samepoint or points. This means there are also a plurality of shortertortuous paths beginning within the first plurality of apertures 121,travelling through first chamber 131, and then up through secondplurality of apertures 122.

[0110] Because first and second chambers 131 and 132 provide a voidspace that can be accessed by a plurality of apertures, they create anumber of different vapor paths, as already noted. However, they alsoprovide a void space in which gas can accumulate and intermix. Thiscreates an additional benefit because the chambers can have differenttemperature gradients, and gases entering or leaving these chambers canhave different temperature gradients as a result of mixing with gascontained in these chambers. Chambers 131 and 132 also act as bufferzones between gas flowing from outside of cap 100 into inner vessel 13and gas flowing from inside of inner vessel 13 to outside of cap 100.

[0111] Cap 100 can also include one or more semi-permeable membranes(not shown in the Figures) to prevent moisture (water vapor) fromentering from entering into the dewar vessel while still allowingvaporous cryogen to exit from the dewar vessel. For example, such amembrane could be used to cover either or both of the first and secondplurality of apertures 121 and 122. (Alternatively, or in addition, asemi-permeable membrane could be placed at any other convenient locationin the vapor path shown in FIG. 5C; however, it is preferable that it beconveniently included as part of cap 100 or inner cap 90. Including asemi-permeable membrane in the cap minimizes the portion of the vaporpath that is restricted by the membrane and provides the membrane with aconvenient structural component for incorporation and structuralintegrity.)

[0112] Accordingly, it will be apparent to those skilled in the art thatstill further changes and modifications in the actual concepts describedherein can readily be made without departing from the spirit and scopeof the disclosed inventions as defined by the following claims.

What is claimed is:
 1. A self-venting cap for a neck of a dewar vessel,comprising: a lower component with a first plurality of apertures; anupper component with a second plurality of apertures, a second chamberand a vent opening; a seal held between the lower and upper componentsthat can form a compression seal about an inner circumference of theneck when the lower and upper components are matingly engaged in acompression seal position; and a first chamber located between the lowerand upper components; wherein vapor inside the dewar vessel can travelin a plurality of tortuous paths when the cap is in the compression sealposition, the plurality of tortuous paths beginning within the neck andthen sequentially travelling up through the first plurality ofapertures, the first chamber, the second plurality of apertures, thesecond chamber and then out the vent opening.
 2. A self-venting cap asrecited in claim 1, further comprising: a third component secured to theupper component so as to define the second chamber and vent openingsbetween the upper and third components.
 3. A self-venting cap as recitedin claim 2, wherein the lower and upper components are matingly engagedby a male and a female thread.
 4. A self-venting cap as recited in claim2, wherein the upper component contains a positioning device on a lowersurface capable of engaging with a second positioning device located ina fixed position relative to the neck such that once the first andsecond positioning devices are engaged, rotation of the third componentin a tightening direction will cause the seal to be squeezed between thelower and upper components to form the compression seal.
 5. Aself-venting cap as recited in claim 2, wherein the lower component, theupper component and the third component are made of cryogenicallycompatible material that is non-metallic and non-conductive.
 6. Aself-venting cap as recited in claim 2, wherein the third component isreleasably secured to the upper component.
 7. A self-venting cap asrecited in claim 1, wherein the vent opening is comprised of a pluralityof vent openings.
 8. A self-venting cap as recited in claim 1, whereinthe plurality of tortuous paths include a plurality of shorter tortuouspaths beginning within the first plurality of apertures, travellingthrough the first chamber, and then up through the second plurality ofapertures.
 9. A self-venting cap as recited in claim 1, wherein there isa plurality of shorter tortuous paths beginning within each of the firstplurality of apertures, travelling through the first chamber, and thenup through at least two of the second plurality of apertures.
 10. Aself-venting cap as recited in claim 1, wherein the seal is comprised ofa silicone material.
 11. A self-venting cap as recited in claim 1,wherein the lower component has an outer circumference that is less thanthe inner circumference of the neck and the first plurality of aperturesis located inside of the outer circumference.
 12. A self-venting cap asrecited in claim 10, wherein the vent opening is located outside of theinner circumference.
 13. A self-venting cap as recited in claim 10,wherein the compression seal is strong enough to support the weight ofthe dewar vessel when it is not charged with a cryogen.
 14. Aself-venting cap as recited in claim 10, wherein the upper component hasan upper outer circumference that is located outside of the innercircumference.
 15. A self-venting cap as recited in claim 14, whereinthe vent opening is located outside of the upper outer circumference.16. A self-venting cap for a neck of a dewar vessel, comprising: a lowercomponent having an outer circumference that is less than the innercircumference of the neck and a first plurality of apertures that islocated inside of the outer circumference; an upper component having anupper outer circumference and a second plurality of apertures, the upperouter circumference being located outside of the inner circumference; aseal held between the lower and upper components that forms acompression seal with an inner circumference of the neck when the lowerand upper components are matingly engaged in a compression sealposition; and a third component secured to the upper component; whereina first chamber is formed between the lower and upper components whenthe lower and upper components are matingly engaged in the compressionseal position; wherein a second chamber and a vent opening locatedoutside of the upper outer circumference are formed between the upperand third components when the lower and upper components are matinglyengaged in the compression seal position; and wherein vapor inside thedewar vessel can travel in a plurality of tortuous paths when the cap isin the compression seal position, the plurality of tortuous pathsbeginning within the neck and then sequentially travelling up throughthe first plurality of apertures, the first chamber, the secondplurality of apertures, the second chamber and then out the ventopening.
 17. A self-venting cap as recited in claim 16, wherein thelower component, the upper component and the third component are made ofcryogenically compatible material that is non-metallic andnon-conductive.
 18. A self-venting cap as recited in claim 17, whereinthere is a plurality of shorter tortuous paths beginning within each ofthe first plurality of apertures, travelling through the first chamber,and then up through at least two of the second plurality of apertures.19. A self-venting cap as recited in claim 16, further comprising: asemi-permeable membrane that prevents moisture from passing through thefirst plurality of apertures while still allowing vaporous cryogen topass through the first plurality of apertures.
 20. A capped dewar vesselassembly, comprising: a dewar vessel having an outer casing and an innervessel with each having openings at their tops connected together by aneck portion forming an evacuable space between the outer casing and theinner vessel and a dewar opening into the inner vessel; a specimenchamber connected to the inner vessel that extends inside the innervessel and is accessed through the dewar opening; and a self-venting capthat restricts access to the specimen chamber when it is in acompression seal position that forms a compression seal with an innercircumference of the neck; wherein vapor inside the dewar vessel cantravel in a plurality of tortuous paths when the cap is in thecompression seal position, the plurality of tortuous paths beginningwithin the dewar opening and then sequentially travelling up through afirst plurality of apertures, a first chamber, a second plurality ofapertures, a second chamber and then out a vent opening.
 21. A cappeddewar vessel assembly as recited in claim 20, wherein there is aplurality of shorter tortuous paths beginning within each of the firstplurality of apertures, travelling through the first chamber, and thenup through at least two of the second plurality of apertures.
 22. Acapped dewar vessel assembly as recited in claim 20, further comprising:a semi-permeable membrane that prevents moisture from entering into thedewar vessel while still allowing vaporous cryogen to exit from thedewar vessel.
 23. A capped dewar vessel assembly as recited in claim 22,wherein the semi-permeable membrane is incorporated into theself-venting cap.